This study investigated the domain and practice of an online community of practice formed by English language teachers (ELTs) on Twitter as a professional learning network (PLN). A "Communities of Practice" framework (Wenger, 1998; Wenger-Trayner & WengerTrayner, 2015) was applied to the qualitative analysis of interviews and publicly accessible social media data of 20 participants. This paper reports on the extent to which members of the PLN use social media for professional purposes and their perceptions of the value of social media in comparison to more traditional means of professional learning: reading ELT textbooks, reading scholarly articles on pedagogy and applied linguistics, and participating in ELT conferences. Findings demonstrate that this PLN functioned as a community of practice that valued social media as a tool in conjunction with the more traditional means of professional learning. Participants said social media had particular advantages, including accessibility, brevity, and low cost. The paper concludes with suggestions for future research and implications for hybrid ELT professional learning practices.